Low slip steering system and improved fluid controller therefor

ABSTRACT

A fluid controller ( 27 ) for use with a fluid pressure operated device ( 45 ) having an inlet ( 47 ) and an outlet ( 49 ) and defining a fluid leakage path therebetween. The controller ( 27 ) includes valving ( 61 ) defining a main fluid path and further defines a fluid bleed passage including a variable bleed orifice (A B ), having a substantially zero flow area when the controller valving ( 61 ) is in its neutral position (N) and in the normal operating position (R), but beginning to open as the valving approaches its maximum displacement position (R-M).

BACKGROUND OF THE DISCLOSURE

[0001] The present invention relates to fluid controllers for use invehicle hydrostatic power steering systems, and more particularly, tosuch controllers which are to be used with fluid pressure operatedsteering actuators of the type which are likely to have noticeableleakage, from the inlet port to the outlet port of the actuator.

[0002] Although the present invention may be utilized in a hydrostaticpower steering system in which the steering actuator is a linearcylinder (either single or double rod end), it is especiallyadvantageous when utilized in a system in which the steering actuator isa rotary motor, and will be described in connection therewith. Examplesof rotary motors which could be utilized as the steering actuator wouldbe a gear motor, or a vane motor, or possibly a gerotor motor of thefixed axis type. Those skilled in the art will understand that theinvention is especially advantageous when used with such a motor as thesteering actuator for reasons which will become apparent subsequently.

[0003] In a typical hydrostatic power steering system, the steeringactuator defines an inlet and an outlet which are connected to thecontrol fluid ports of a fluid controller, which is also typicallyreferred to as a steering control unit (SCU). The steering actuatorreceives at its inlet a flow of metered, pressurized fluid from the SCU,which results in an output motion which, in turn, results in appropriatemovement of the steered wheels.

[0004] If the steering actuator is a rotary motor, there is likely to bethe potential for a noticeable amount of internal leakage between theinlet and the outlet, effectively bypassing the rotating group. Theamount of leakage which can or does occur during normal steeringoperations does not represent a significant problem in terms of theoverall performance of the steering system.

[0005] However, it has been found that there may be a performanceproblem whenever one of the steered wheels of the vehicle engages anobject, such as a curb, or for some other reason, the system iseffectively steering “against-the-stops”. Whenever a steeragainst-the-stops type of situation occurs, such that there is no rotaryoutput from the rotating group of the motor, a substantial amount of thefluid communicated to the inlet of the motor will leak internally withinthe motor, bypassing the rotating group, and flowing to the outlet port.

[0006] One result of such internal leakage within the steering actuatoris that the SCU continues to communicate metered, pressurized fluid tothe inlet of the actuator. Thus, even though no additional turningmotion is being transmitted to the steered wheels, the operator is stillable to rotate the steering wheel. Such ongoing ability to rotate thesteering wheel, without any corresponding change in the position of thesteered wheels, appears to the vehicle operator as steering wheel “slip”which is considered a very undesirable characteristic of a steeringsystem. Typically, vehicle manufacturers specify a maximum, permissiblesteering wheel slip, generally in terms of the maximum permissiblenumber of rotations of the steering wheel over a given time period. Forexample, a typical specification for wheel slip would be somewhere inthe range of about two to about five revolutions per minute.

[0007] As is well know to those skilled in the art of fluid controllers,a typical fluid controller of the type to which the present inventionrelates includes some sort of controller valving defining a neutralposition (when there is no steering input), a normal operating position(when normal steering is occurring) and a maximum displacement position,i.e., the maximum opening (flow area) of the valving. Whenever thesteering system is in a steer against-the-stops type of situation, thecontroller valving is typically displaced to the maximum displacementcondition. The conventional neutral return spring, which is present inmost such fluid controllers, tends to return the valving toward theneutral position, but is at its fully deflected condition when thevalving is in the maximum displacement condition.

[0008] Fluid controllers of the type which can utilize the presentinvention typically include some sort of fluid actuated arrangement forimparting follow-up movement to the controller valving, tending toreturn the valving from its normal operating position toward its neutralposition. In the fluid controllers produced and sold by the assignee ofthe present invention, the fluid actuated arrangement is a fluid meterwhich comprises a gerotor gear set. The gerotor gear set includes aninternally toothed ring and an externally toothed star, disposedeccentrically within the ring. One possible solution to the apparentslip problem discussed above is to increase the tip clearance of theteeth in the gerotor gear set, thus communicating some flow through thefluid meter to the control fluid port, to compensate for the leakagewithin the actuator. Unfortunately, such an increase in the tipclearance within the gerotor gears has been found to permit a conditionknown as “feed-through” in which there is a flow of fluid through thefluid meter even at times when such is not desired.

BRIEF SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the present invention to providean improved hydrostatic power steering system of the type describedabove which overcomes, in the situation described, the apparent wheelslip of the fluid controller.

[0010] It is a more specific object of the present invention to providean improved fluid controller for use in such a system in which the fluidcontroller is able effectively to compensate for the leakage which isoccurring at the steering actuator.

[0011] The above and other objects of the invention are accomplished bythe provision of a fluid controller operable to control the flow offluid from a source of pressurized fluid to a fluid pressure operateddevice having an inlet and an outlet and defining a fluid leakage paththerebetween. The fluid controller is of the type including a housingdefining an inlet port for connection to the source of pressurizedfluid, a return port for connection to a system reservoir, and a controlport for connection to the inlet of the fluid pressure operated device.The controller includes valving disposed in the housing and defining aneutral position, a normal operating position, and a maximumdisplacement position. The housing and the valving cooperate to define amain fluid path providing fluid communication between the inlet port andthe control port when the valving is in the normal operating position.The controller includes a fluid actuated means for imparting follow upmovement to the valving, tending to return the valving from its normaloperating position toward the neutral position, the follow up movementbeing proportional to the volume of fluid flow through the main fluidpath. The main fluid path includes a first variable flow control orificehaving a minimum flow area when the valving is in the neutral position,and an increasing flow area as the valving is displaced through thenormal operating position toward the maximum displacement position.

[0012] The improved fluid controller is characterized by the valvingdefining a fluid bleed passage having an upstream portion in fluidcommunication with the main fluid path at a location upstream of thefirst variable flow control orifice, and a downstream portion in fluidcommunication with the main fluid path downstream of the fluid actuatedmeans. The fluid bleed passage includes a variable bleed orifice havinga substantially zero flow area when the valving is in the neutralposition and in the normal operating position. The variable bleedorifice begins to open as the valving approaches the maximumdisplacement position.

[0013] Therefore, in accordance with the present invention, whenever thesteering system is in a steer against-the-stops situation, and thevalving is in the maximum displacement position, a small amount of fluidis communicated through the fluid bleed passage of the fluid controllerto compensate for the amount of leakage anticipated through the steeringactuator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a hydraulic schematic of a hydrostatic power steeringsystem including a fluid controller of the type which may utilize thepresent invention.

[0015]FIG. 2 is a greatly enlarged hydraulic schematic of the fluidcontroller of the present invention.

[0016]FIG. 3 is an axial cross-section of a fluid controller of the typeto which the present invention relates.

[0017]FIG. 4 is a flat view of the spool valve of the fluid controllershown schematically in FIG. 2, including the present invention.

[0018]FIG. 5 is a flat view of the sleeve valve of the fluid controllershown schematically in FIG. 2, for use as part of the present invention

[0019]FIG. 6 is an enlarged, fragmentary overlay view of the valvingshown in FIGS. 4 and 5, and with the valving in its neutral position.

[0020]FIG. 7 is an enlarged, fragmentary overlay view of the valving,similar to FIG. 6, but with the valving in its normal operatingposition, in a right turn.

[0021]FIG. 8 is an enlarged, fragmentary overlay view of the valvingshown in FIG. 6, but with the valving in its maximum displacementposition, and still in a right turn, and illustrating the operation ofthe present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] Referring now to the drawings, which are not intended to limitthe invention, FIG. 1 is a hydraulic schematic of a vehicle hydrostaticpower steering system including a fluid controller of the type to whichthe present invention applies. The system includes a source ofpressurized fluid, generally designated 11, which in the subjectembodiment, and by way of example only, includes a fluid pump 13 and aload sensing priority type flow control valve 15. The fluid pump 13 isshown herein as a fixed displacement pump for ease of illustration,having its inlet connected to a system reservoir 17.

[0023] As is well know to those skilled in the art, because of thepresence of the priority valve 15, the source 11 includes a pair offluid outlets including a priority outlet 19 and an excess flow outlet21. For simplicity, the excess flow outlet 21 is shown connected to anauxiliary load circuit, represented schematically by a variable orifice23. The priority outlet 19 is connected by means of a conduit 25 to afluid controller, generally designated 27. It should be noted that thereference numeral “27” will be used throughout in reference to the fluidcontroller, even though the schematic representation in FIG. 1 and theaxial cross-section in FIG. 3 do not actually illustrate the presentinvention.

[0024] Referring still primarily to FIG. 1, the fluid controller 27includes a housing 29 (see FIG. 3) which defines an inlet port 31, towhich is connected the conduit 25. The housing 29 also defines a returnport 33 which is connected to the system reservoir 17 by means of aconduit 35. The housing 29 further defines a load signal port 37 (shownonly in FIG. 1) from which a load signal 39 is communicated to thepriority valve 15 in a manner well know to those skilled in the art.

[0025] The housing 29 of the fluid controller 27 also defines a pair ofcontrol (motor) fluid ports 41 and 43 which are connected to theopposite ports of a steering actuator, shown herein as comprising arotary fluid pressure operated motor 45. Assuming a right turn, thecontrol port 41 is connected to a motor inlet 47 while a motor outlet 49is connected to the other control port 43. The output of the rotarymotor 45 is shown schematically in FIG. 1 as a shaft 51 which transmitstorque (steering output motion) to a gear train, generally designated53, by means of which the rotation of the shaft 51 is transmitted into ahigher torque rotation of a steered wheel support structure 55. Attachedrotatably to the support structure 55, and driven thereby, is a steeredwheel 57, it being understood that, in a typical vehicle installation,there would be two of the steered wheels 57, such that the structureassociated with the steered wheel 57, and shown in FIG. 1, would beduplicated. In some vehicle applications, there may be as many as foursteered wheels, and the present invention is equally adaptable to suchapplications.

[0026] Referring now to FIG. 2, in conjunction with FIG. 1, it may beseen that the fluid controller 27 includes controller valving, generallydesignated 61, a general function of which is to control the flow offluid from the inlet port 31 to the control port 41 (assuming a rightturn), and at the same time, control the flow of returning fluid fromthe opposite control port 43 to the return port 33. Such control offluid flow within the fluid controller 27 is accomplished in response torotation by the vehicle operator of a steering wheel, representedschematically in FIGS. 1 and 2 as an input 63.

[0027] The fluid controller 27 may be of the general type illustratedand described in U.S. Pat. No. 5,638,864, assigned to the assignee ofthe present invention and incorporated herein by reference. Morespecifically, the fluid controller 27 includes controller valving 61which is moveable from its neutral position (“N” in FIG. 2) to either aright turn position (“R” in FIG. 2) or a left turn position (“L” in FIG.2). Those skilled in the art will understand that the normal operatingpositions of the controller valving 61 are those positions disposedimmediately on either side of the neutral position N, in FIG. 2. Whenthe valving 61 is in either of the turn positions (R or L), thepressurized fluid flowing through the valving 61 also flows through afluid meter 65, one function of which is to measure (meter) the properamount of fluid to be communicated to the appropriate control port 41 or43. As is well know to those skilled in the art, the other function ofthe fluid meter 65 is to provide follow-up movement to the valving 61,such that the valving is returned to its neutral position N after thedesired amount of fluid has been communicated to the steering actuator.As is shown in FIGS. 1 and 2, such follow-up movement is achieved bymeans of a mechanical follow-up connection, from the fluid meter 65 tothe valving 61, the mechanical follow-up connection being shownschematically at 67.

[0028] As is also shown schematically in FIGS. 1 and 2, the controllervalving 61 defines a plurality of variable orifices whenever the valvingis moved from its neutral position N to one of its normal operatingpositions R or L. These variable orifices will be described in greaterdetail subsequently, in conjunction with the detailed description ofFIGS. 6 through 8. Also shown schematically in FIG. 2 are two additionalpositions of the valving 61 which are not shown in FIG. 1, and whichillustrate one aspect of the present invention. Adjacent the normaloperating position in the right turn R is the right turn maximumdisplacement condition (“R-M”) and similarly, adjacent the normaloperating position in the left turn L is the left turn maximumdisplacement position (“L-M”). These positions of the valving will alsobe described in greater detail, in connection with the description ofFIG. 8.

Fluid Controller 27

[0029] Referring now primarily to FIG. 3, the construction of the fluidcontroller 27 will be described in some detail. The controller comprisesseveral sections including the housing section 29, a port plate 69, asection comprising the fluid meter 65, and an end cap 71. These sectionsare held together in tight, sealing engagement by means of a pluralityof bolts 73, only one of which is shown in FIG. 3, and which are inthreaded engagement with the housing 29. The housing 29 defines theinlet port 31, the return port 33, and the control ports 41 and 43. Thehousing 29 also defines the load signal port 37 which is not shown inFIG. 3.

[0030] Rotatably disposed within a valve bore 75 defined by the housing29 is the valving arrangement 61. In the subject embodiment, and by wayof example only, the valving 61 comprises a primary, rotatable valvemember 77 (hereinafter also the “spool”), and a cooperating, relativelyrotatable follow-up valve member 79 (hereinafter also the “sleeve”). Atthe forward end of the spool 77 is a portion having a reduced diameterand defining a set of internal splines 81 which provide for a directmechanical connection between the spool 77 and the steering wheel 63.The spool 77 and sleeve 79 will be described in greater detailsubsequently.

[0031] The fluid meter 65 may be of a type well known in the art andincludes herein, and by way of example only, an internally toothed ring83, and an externally toothed star 85. The star 85 defines a set ofinternal splines 87, and in splined engagement therewith is a set ofexternal splines 89, formed at the rearward end of a main drive shaft91. The shaft 91 has a bifurcated forward end permitting drivingconnection between the shaft 91 and the sleeve 77, by means of a pin 93passing through a pair of pin openings 95 in the spool 77. Thus,pressurized fluid flowing through the valving 61, in response torotation of the steering wheel 63 and the spool 77 flows through thefluid meter 65, causing orbital and rotational movement of the star 85within the ring 83. Such movement of the star 85 causes follow-upmovement of the sleeve 79, by means of the drive shaft 91 and pin 93(which together comprise the follow-up connection 67 of FIGS. 1 and 2).This movement of the star 85 maintains a particular relativedisplacement between the spool 77 and sleeve 79, for a given, constantrate of rotation of the steering wheel. A plurality of leaf springs 97extends through an opening in the sleeve 79, biasing the sleeve 79toward its neutral position relative to the spool 77, in a manner whichis conventional and well known in the art.

[0032] It may be seen in FIG. 3 that the housing 29 defines four annularchambers surrounding the sleeve 79, to provide fluid communicationbetween the outer surface of the sleeve 79 and the various ports 31, 33,41 and 43. The various annular chambers are designated by the referencenumeral of the respective port, accompanied by the letter “c”. Thoseskilled in the art will understand the interaction of the annularchambers 31 c, 33 c, 41 c and 43 c with the valving 61.

[0033] The toothed interaction of the star 85, orbiting and rotatingwithin the ring 83, defines a plurality of expanding and contractingfluid volume chambers, and adjacent each chamber, the port plate 69defines a fluid port (not shown in FIG. 3) and adjacent thereto, thehousing 29 provides a plurality of axial bores (also not shown in FIG.3), each of which is in open communication at one end with the fluidports in the port plate 69, and at its other end, with the valve bore75.

Valving Arrangement 61

[0034] Referring now primarily to FIGS. 4 and 5, the spool 77 and thesleeve 79 will be described in greater detail. It should be noted thatFIG. 4 illustrates the outer surface of the spool 77, while FIG. 5illustrates both the outer surface of the sleeve 79 and several featureswhich are disposed on the inner surface of the sleeve 79, and therefore,are in a valving relationship with the features disposed on the outersurface of the spool 77. It should be understood by those skilled in theart that both the spool 77 and the sleeve 79 include a number offeatures or elements which are conventional, but are not directlyinvolved in the operation of the invention, and therefore, do not bearreference numerals in FIGS. 4 and 5, are not described hereinafter.

[0035] The spool 77 defines an annular groove 101, and in communicationtherewith, a plurality of axial slots 103. Circumferentially displacedfrom each of the axial slots 103 is a longer axial slot 105, andcircumferentially aligned with each of the axial slots 103 is an evenlonger axial slot 107, the function of which will be describedsubsequently. To the right of the annular groove 101, the spool 77defines a plurality of axial, open-center slots 109, each of which has,adjacent thereto, a slot 111 which is in open communication, toward itsright end, with the interior of the spool 77.

[0036] The sleeve 79 defines a plurality of pressure ports 113, incommunication with the annular chamber 31 c and therefore, the pressureports 113 receive pressurized, un-metered fluid from the source 11. Tothe left of the ports 113 is a plurality of meter ports 115, whichcommunicate between the valving arrangement 61 and the expanding andcontracting fluid volume chambers of the fluid meter 65, through theaxial bores defined by the housing 29, in a manner well know to thoseskilled in the art. In the subject embodiment, and by way example only,the star 85 has six external teeth and the ring 83 has seven internalteeth, so there are 12 of the meter ports 115. Disposed to the left ofthe meter ports 115 is a plurality of cylinder ports 117, incommunication with the annular chamber 41 c, and further to the left, aplurality of cylinder ports 119, in communication with the annularchamber 43 c.

Operation of Valving 61

[0037] It is believed that the basic operation of the controller 27 andthe valving 61 described thus far, all of which is conventional, shouldbe readily apparent in view of the teachings of the above incorporatedpatent. However, the operation of the valving 61 will be describedbriefly, partially to relate the structure illustrated in FIGS. 3-8 withthe schematics of FIGS. 1 and 2. The operation of the valving 61 will bedescribed in connection with FIGS. 6-8, which are enlarged (relative toFIGS. 4 and 5), and are fragmentary overlay views of the spool 77(except where visible through an opening in the sleeve 79) and thesleeve 79 (but showing only those features present on the inside surfaceof the sleeve).

[0038] Referring now primarily to FIG. 6, when the valving 61 is in theneutral position N (no rotation of the steering wheel occurring), inletfluid is communicated from the inlet port 31 into the annular chamber 31c. The pressure ports 113 are in open communication with the annularchamber 31 c, but there is no flow through the pressure port 113,because, in the neutral position shown in FIG. 6, the ports 113 areblocked from communication with any of the slots or grooves defined bythe spool 77, i.e., the ports 113 are blocked by the outer cylindricalsurface of the spool 77.

[0039] Referring now primarily to FIG. 7, when the steering wheel isrotated clockwise by the operator (a right turn condition), the spool 77is displaced from its neutral position, relative to the sleeve 79.Within each pair of pressure ports 113, one of the ports 113 begins toapproach, and then overlap one of the axial slots 103, while the otherport 113 moves away from its respective axial slot 103. The areas ofoverlap of the pressure ports 113 and the axial slots 103 define avariable flow control orifice, the composite of these individualvariable orifices comprising a main variable flow control orifice A1(see FIG. 2). At the same time, each of the axial slots 103 begins tocommunicate with one of the meter ports 115, the area of overlaptherebetween defining a variable orifice, and the composite of thesecomprising a variable flow control orifice A2, as is well known to thoseskilled in the art and is not shown in the schematics of FIGS. 1 and 2.Every other meter port 115 is in communication with one of axial slots103, while the alternate meter ports 115 are now in communication withthe longer axial slots 105. The area of overlap between each of thesealternate meter ports 115 and the respective axial slots 105 defines avariable orifice, and the composite of these comprises a variable flowcontrol orifice A3, also not shown in the schematics of FIGS. 1 and 2.As is well known to those skilled in the art, the fluid which flowsthrough the A2 orifice, and from there to the expanding volume chambersof the fluid meter 65 is pressurized, un-metered fluid, while the fluidwhich flows from the contracting volume chambers of the fluid meter 65through the A3 orifice is pressured, metered fluid.

[0040] With the spool 77 and the sleeve 79 in the relative positionshown in FIG. 7, i.e., in the normal operating position R, each of thelonger axial slots 105 begins to communicate with an adjacent one of thecylinder ports 117, the overlap therebetween defining a variableorifice, and the composite of these individual orifices comprising avariable flow control orifice A4. As is well known to those skilled inthe art, the cylinder ports 117 are in communication, by means of theannular chamber 41 c, with the control fluid port 41, and with what is,in a right turn condition, the inlet 47 of the rotary motor 45. Fluidreturning from what is now the outlet 49 of the rotary motor 45 entersthe control fluid port 43, then flows through the annular chamber 43 c,and then through the cylinder ports 119 which are now in fluidcommunication with the axial slots 107. The overlap of the ports 119 andthe axial slots 107 defines a variable orifice, the composite of theseindividual variable orifices comprising a variable flow control orificeA5. Therefore, the flow path through the variable flow control orificesA1, A2, fluid meter 65, variable flow control orifices A3, A4, fluidmotor 45, and variable flow control orifice A5, as just describedcomprises the “main fluid path” in the right turn condition. It shouldbe noted that the architecture of the valving of some fluid controllersdoes not require or include the variable flow control orifices A2 and A3(i.e., those on the inlet and outlet sides, respectively, of the fluidmeter 65). Alternatively, in some controller architectures, the A2 andA3 orifices are fixed orifices, rather than variable. All that isrequired for the present invention is to have one flow control orifice(e.g., the Al orifice) between the inlet port 31 and the fluid meter 65,and one more flow control orifice (e.g., A4) between the fluid meter 65and the control (motor) fluid port 41 or 43.

[0041] Referring now primarily to FIG. 8, in conjunction with FIG. 4, ofthe six longer axial slots 105, at least one is provided with an axiallyextending recess 121, and in the subject embodiment, and by way ofexample only, there are three of the recess 121. In the subjectembodiment, and again by way of example only, valving 61 has a maximumdeflection (displacement) of about 10 degrees. Therefore, as the valving61 approaches the maximum displacement position (R-M in FIG. 2), i.e.,when the relative displacement of the spool and sleeve is about 9degrees (the position shown in FIG. 8) the various flow control orificesA1 through A5 have reached, or nearly reached, their maximum flow area.For ease of further illustration and description, the pressure ports arelabeled 113-R and 113-L. The pressure port 113-R is the one whichoverlaps the axial slot 103 to define the A1 orifice in a right turncondition, while the pressure port 113-L is one the which moves awayfrom its respective axial slot 103, but would overlap its respectiveaxial slot 103 to form the Al orifice in a left turn condition.

[0042] As is seen in FIG. 8, as the relative position of the spool 77and the sleeve 79 approaches the maximum displacement position (R-M inFIG. 2), the pressure port 113-L begins to overlap the respectiveaxially extending recess 121, the area of overlap therebetween defininga variable orifice, and the composite of the three overlaps (becausethere are three of the recesses 121) comprises a variable bleed orificeAB. Therefore, at the three locations on the spool 77 wherein the axialslot 105 includes one of the axially extending recesses 121,communication of pressurized un-metered fluid through the pressure port113, and then through the recess 121 and into the axial slot 105comprises a fluid bleed, and those three locations cumulatively comprisea fluid bleed passage. As is best shown schematically in FIG. 2, thefluid bleed passage, including the variable lead orifice AB has anupstream portion in communication with the main fluid path at a locationupstream of the first variable fluid control orifice A1, and adownstream portion in communication with the main fluid path downstreamof the fluid meter 65, but upstream (preferably) of the variable flowcontrol orifice A4. Note that in FIG. 2, in the R-M and L-M positions,the flow control orifice A4 is shown schematically as a fixed orifice,purely for ease of illustration.

[0043] In operation, and is well known to those skilled in the art, mostof the steering occurs with the valving 61 in the normal operatingposition, as is represented in FIG. 7, i.e., with the spool 77 displacedrelative to the sleeve 79 by a displacement in the range of about 2degrees to about 8.5 or 9 degrees. Very little steering occurs while thevalving is in the maximum displacement position of FIG. 8 in which, witha maximum possible deflection of 10 degrees, the valving is displace byat least 8.5 or 9 degrees. However, as was described in the BACKGROUNDOF THE DISCLOSURE, whenever the steered wheels 57 engage a curb or a rutor some other obstruction, which resists further movement of the steeredwheels, or in a steer against-the-stops situation, the torque loadexerted by the steered wheels on the rotary motor 45 will result in thevalving 61 of fluid controller 27 being displaced to the maximumdisplacement condition (R-M) illustrated in FIG. 8. As was alsodescribed in the BACKGROUND OF THE DISCLOSURE, whenever the steeringsystem is in the condition described above, it is typical for there tobe a very noticeable internal leakage path between the inlet and theoutlet of the rotary motor 45. However, by means of the presentinvention, a sufficient quantity of fluid is communicated through thefluid bleed passage, and through the variable bleed orifice AB, andjoins the fluid which flows through the main fluid path of the fluidcontroller 27, this combination of the main path fluid and the bleedfluid together flowing to the control port 43, and from there to theinlet of the rotary motor 45.

[0044] The invention has been described in great detail in the foregoingspecification, and it is believed that various alterations andmodifications of the invention will become apparent to those skilled inthe art from a reading and understanding of the specification. It isintended that all such alterations and modifications are included in theinvention, insofar as they come within the scope of the appended claims.

1. A fluid controller operable to control the flow of fluid from asource of pressurized fluid to a fluid pressure operated device havingan inlet and an outlet and defining a fluid leakage path therebetween;said fluid controller being of the type including a housing defining aninlet port for connection to the source of pressurized fluid, a returnport for connection to a system reservoir, and a control port forconnection to said inlet of said fluid pressure operated device, valvingdisposed in said housing and defining a neutral position (N), a normaloperating position (R) and a maximum displacement position (R-M), saidhousing and said valving cooperating to define a main fluid pathproviding fluid communication between said inlet port and said controlport when said valving is in said normal operating position (R); fluidactuated means for imparting follow-up movement to said valving, tendingto return said valving from said normal operating position (R) towardsaid neutral position (N), said follow-up movement being proportional tothe volume of fluid flow through said main fluid path, said main fluidpath including a first variable flow control orifice, having a minimumflow area when said valving is in said neutral position (N), and anincreasing flow area as said valving is displaced through said normaloperating position (R) toward said maximum displacement position (R-M);characterized by: (a) said valving defining a fluid bleed passage havingan upstream portion in fluid communication with said main fluid path ata location upstream of said first variable flow control orifice, and adownstream portion in fluid communication with said main fluid pathdownstream of said fluid actuated means; and (b) said fluid bleedpassage including a variable bleed orifice having a substantially zeroflow area when said valving is in said neutral position (N) and in saidnormal operating position (R), said variable bleed orifice beginning toopen as said valving approaches said maximum displacement position(R-M).
 2. A fluid controller as claimed in claim 1, characterized bysaid valving comprising a primary, rotatable valve member and acooperating, relatively rotatable follow-up valve, said primary andfollow-up valve members defining said neutral position (N) relative toeach other, said fluid controller including a biasing spring operable tobias said primary and follow-up valve members toward said neutralposition (N) relative to each other.
 3. A fluid controller as claimed inclaim 2, characterized by said primary and follow-up valve members beingdisplaceable from said neutral position (N) to said normal operatingposition (R) relative to each other in opposition to the force of thebiasing spring.
 4. A fluid controller as claimed in claim 3,characterized by said primary and follow-up valve members beingdisplaceable from said neutral position (N) through said normaloperating position (R) to said maximum displacement position (R-M), saidmaximum displacement position corresponding to the maximum possiblerelative displacement of said primary and follow-up valve members.
 5. Afluid controller as claimed in claim 1, characterized by said follow-upvalve member defining a first pressure port and a second pressure portboth of said pressure ports being in fluid communication with said inletport when said valving is in said normal operating position (R), saidprimary valve member defining a first axial slot, fluid communicationbetween said first pressure port and said first axial slot comprisingsaid first variable flow control orifice.
 6. A fluid controller asclaimed in claim 5, characterized by said primary valve member defininga second axial slot comprising part of said main fluid path, downstreamof said first variable flow control orifice, said second pressure portbeing out of fluid communication with said second axial slot when saidvalving is in said normal operating position (R) but being in fluidcommunication with said second axial slot as said valving approachessaid maximum displacement position (R-M).